1. Field of the Invention
The present invention relates generally to semiconductor laser devices and methods of fabricating the same and particularly to monolithic semiconductor laser devices used as a source of light for optical discs of different standards and methods of fabricating the same.
2. Description of Related Art
In recent years, recording media providing enhanced recording densities and reproduction devices therefor are increasingly developed. For example, the digital versatile disc (DVD) is increasingly used in a variety of areas as an optical disc capable of recording/reproducing motion images and an increasing demand therefor in future is expected. Recently, there is an increasing need by users for developing a drive device having a function also capable of recording/reproducing conventional compact discs (CDs).
To implement this drive device there have been proposed a hybrid laser apparatus incorporating in a single package a red laser device of a wavelength of the 600 nm band used to record/reproduce a DVD and an infrared laser device of a wavelength of the 700 nm band used for a laser to record/reproduce a CD, and a monolithic laser device having two laser portions formed on a single substrate to oscillate red laser light of a wavelength of the 600 nm band and infrared laser light of a wavelength of the 700 nm band.
If the hybrid laser apparatus is used for the drive device, however, it is difficult to improve precision of a light emission point, which is an important factor for optional pickup, since the two laser devices are incorporated in the single package. Thus, for the drive device, using a monolithic laser device allowing a highly controllable position of a light emission point is considered effective.
FIG. 11 is a schematic perspective view of a conventional monolithic semiconductor laser device. In FIG. 11, a conventional monolithic semiconductor laser device 500 includes an infrared laser portion 502 having a double hetero structure for CDs and a red laser portion 503 having a double hetero structure for DVDs for a total of two laser portions. Conventional monolithic semiconductor laser device 500 is fabricated as follows: with reference to FIG. 12, initially to form red laser portion 503 an AlGaInP based semiconductor layer is grown. Then outside the growth furnace the AlGaInP based semiconductor layer that has grown in a region other than that to be provided with red laser portion 503 is etched away and subsequently to form infrared laser portion 502 an AlGaAs based semiconductor layer is grown, for example. Herein, the laser portions are both formed by metal-organic chemical vapor deposition (MOCVD) and have p type dopant of zinc (Zn) introduced therein.
In the conventional monolithic semiconductor laser device, however, the laser portion's light emission efficiency can decrease, and in a current-voltage characteristic an abnormality can be caused or a similarly impaired laser characteristic can be provided. In monolithic semiconductor laser devices, in particular, if one laser portion exhibits a poor laser characteristic and the other laser portions present a satisfactory characteristic the entirety of the semiconductor laser device still would be regarded as defective, resulting in decreased production yields.